Field of the Invention
The present application relates to an electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
Description of the Related Art
Electrophotographic photosensitive members used in process cartridges and electrophotographic apparatuses contain an organic photoconductive substance (charge generating substance). Such an electrophotographic photosensitive member is superior in productivity because the layer thereof can be easily formed by application of a coating material. In general, an electrophotographic photosensitive member includes a support and a photosensitive layer on the support.
The photosensitive layer often has a multilayer structure including a charge generating layer containing a charge generating substance, and a hole transporting layer containing a hole transporting substance on the charge generating layer.
A more long-life electrophotographic apparatus has recently been demanded. Accordingly, it is desired to enhance the durability of the electrophotographic photosensitive member against mechanical and electrical degradation.
Japanese Patent Laid-Open No. 10-39521 discloses a technique for enhancing the mechanical strength in which the binding resin used in the hole transporting layer is replaced from a polycarbonate resin to a polyester resin to suppress mechanical degradation. For increasing the lifetime, in addition, the thickness of the hole transporting layer is increased.
In the case of a hole transporting layer containing an aromatic polyester resin produced from an aromatic dicarboxylic acid and an aromatic diol, however, if the thickness thereof is increased, photo memory is liable to occur. Photo memory is a phenomenon caused by a potential difference between a portion exposed to light and an unexposed portion. When an electrophotographic photosensitive member is exposed to light, charges retain in the exposed portion and thus cause a potential difference.
In order to achieve both the enhancement of durability and the decrease of photo memory for an electrophotographic photosensitive member, a specific structure has been devised for the aromatic polyester resin. Japanese Patent Laid-Open No. 2005-250503 discloses an aromatic polyester resin whose aromatic diol portion has a specific structure. Japanese Patent Laid-Open No. 2008-203528 discloses an aromatic polyester resin whose dicarboxylic acid portion has a specific structure.
According to a study of the present inventors, however, these aromatic polyester resins were not able to reduce photo memory sufficiently in some cases. Further improvement of aromatic polyester resin is desired.